1. Field of the Invention
The present invention relates to an improved infrared microscopic spectrometer.
2. Description of Related Art
FIG. 1 shows a conventional general infrared microscopic spectrometer. Infrared rays from a light source 1 are directed to a sample 3 through a condenser mirror 2. The light transmitted through the sample 3 is focused into an image by an object mirror 4. The image is transmitted to a spectrometer system 5 to obtain a spectrum and then to a display device 6 to conduct an analysis.
Another well-known method of infrared spectrometry, the ATR (Attenuated Total Reflection) method, is used for a substance having an extraordinarily strong absorption, and thus difficult to obtain a transmission spectrum or, in the case where it is difficult to prepare a sample, to obtain the transmission spectrum.
FIG. 2 shows the basic parts of a general infrared spectrometer using the ATR method. Reference numerals 7, 8 designate a collecting mirror. Reference numerals 9, 10 designate a mirror. An optical reflecting medium having a high refractive index; for example, an ATR crystal 11 made of a refractive material, such as KRS-5, germanium and silicon, is located in an optical path between mirrors 9, 10. A sample 12 is placed on one surface of ATR crystal 11.
When infrared rays 13 from a light source (not shown) are directed upon the ATR crystal 11 by way of collecting mirror 7 and mirror 9, the rays are reflected by the contact surface between crystal 11 and sample 12. Infrared rays having certain wavelengths are absorbed by the ingredient in sample 12 that is to be measured. The infrared rays, which have passed through the ATR crystal 11, after being reflected, are directed to a spectrometer (not shown) by way of mirror 10 and collecting mirror 8 to obtain the spectrum corresponding to the ingredient to be measured.
Let us review the optical system in the above two infrared spectrometers. In the infrared microscopic spectrometer of FIG. 1, infrared rays from a light source 1 are directed to be incident upon a sample 3 by means of a condenser mirror 2. The transmitted light is then focused into an image. The condenser mirror 2 and an object mirror 4 must be coaxially arranged.
On the other hand, in the ATR method of FIG. 2, the optical axis of infrared rays incident upon the ATR crystal 11 does not coincide with the optical axis of infrared rays being reflected. As a result, the ATR method has not been applied to infrared microscopic spectrometry.
According to the prior art, for samples having strong absorption only the ATR method can be used. Microscopic spectrometry could not be used. This has led to remarkably reduced efficiency. The present invention overcomes this difficulty.